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Study on the mass transfer characteristics in an AOD converter bath with side and top combined blowing

WEI Ji-he,ZUO Huai-ying (College of Materials Science and Engineering,Shanghai University,Shanghai 200072,China)  
The mass transfer characteristics in the bath during the AOD refining process with the conditions of side and top combined blowing were investigated.The experiments were conducted on a water model unit of 1/4 linear scale for a 120 t side and top combined blowing AOD converter.Sodium chloride powder of analytical purity was used as the flux for blowing,and the mass transfer coefficient of solute(NaCl) in the liquid was determined under the conditions of the AOD process.The effects of the gas flow rates of side and top blowing processes,the position and number of side tuyere,the powder flux particle(bubble) size and others on the characteristics were examined.The results indicated that,under the conditions of the present work,the mass transfer coefficient of solute in the bath liquid is in the range of(7.31×10-5~3.84×10-4)m/s.The coefficient increases non-linearly with increasing angle between each tuyere,for the simple side blowing process at a given side tuyere number and gas side blowing rate.The gas flow rate of the main tuyere has a governing influence on the characteristics,and the gas jet from the top lance decreases the mass transfer rate,the relevant coefficient being smaller than that for a simple side blowing.Also,in the range of particle(bubble) size used in the present work and with all other factors being constant,raising particle(bubble) size increases the coefficient.Excessively fine powder(bubble) sizes are not advantageous to strengthening the mass transfer.Corresponding to the oxygen top blowing rate specified by the real technology used,the side tuyere arrangements of 7 and 6 tuyeres with an angular separation of 22.5° and 27° between each tuyere,as well as 5 tuyere with an angle of 22.5° between each tuyere can all provide a larger mass transfer rate.Considering respectively the relative velocity of the particles to the liquid,the energy dissipation caused by the fluctuation in the velocity of the liquid in turbulent flow and regarding the mass transfer as that between a rigid bubble and molten steel,the related dimensionless relationships for the coefficient were obtained.
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